<template>
    <ul class="list">
        <li class="item" v-for="(item,key) of cities" 
         ::key="key" 
         :ref="key"
         @click="handleLetterClick"
         @touchstart="handleTouchStart" 
         @touchmove="handleTouchMove"
         @touchend='handleTouchEnd'
         >{{key}}</li>
    </ul>     
    </template>

<script>
    export default {
        name: 'CityAlphabet',
        props: {
            cities: Object
        },
        computed: {
            letters() {
                const letters = [];
                for (let i in this.cities) {
                    letters.push(i)
                }
                return letters;
            }
        },
        data() {
            return {
                touchStatus: false
            }
        },
        methods: {
            handleLetterClick(e) {
                this.$emit('change', e.target.innerText)
            },
            handleTouchStart() {
                this.touchStatus = true;
            },
            handleTouchMove(e) {
                if (this.touchStatus) {
                    const startY = this.$refs['A'][0].offsetTop;
                    const touchY = e.touches[0].pageY - 79;
                    const index = Math.floor((touchY - startY) / 20)
                    if (index >= 0 && index < this.letters.length) {
                        this.$emit('change', this.letters[index]);
                    }
                }
            },
            handleTouchEnd() {
                this.touchStatus = false;
            }
        }
    }
</script>

<style lang="scss" scoped>
    @import '~@/assets/style/varibles.scss';
    .list {
        display: flex;
        flex-direction: column;
        justify-content: center;
        position: absolute;
        top: 1.58rem;
        right: 0;
        bottom: 0;
        width: .4rem;
        .item {
            line-height: .4rem;
            text-align: center;
            color: $bgColor;
            cursor: pointer;
        }
    }
</style>